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carbon steel ball bearing p g to pierce the casing. The bombs were installed at intervals of ten feet below the steel liner (from 58 feet to 126 feet), and at five feet intervals within the ' liner (from the surface to 58 feet). The bombs consisted of bundled up detonation cord such that a total of seven strands of cord produced a six to eight inch long explosive package. ' Once the charge was installed, a cement sl was installed in the well via tremmie pipe. g �Y pp The cement was brought to the surface of the ground and the tremmie pipe was removed. ' The charge was set off in a series of three detonations. The first detonation consisted of the lower third of the charge, the second followed 1.5 seconds later and detonated the middle third, and the third detonation, also delayed 1.5 seconds, consisted of the upper ' third of the charge. ' Almost no grout was lost from the well casing following the detonations, however the level of grout fell significantly within the well casing. Additional cement grout was then added to bring the cement slurry to the ground surface. ' Representatives from the San Joaquin County Environmental Health Department were on-site during installation, detonation, and finish grouting of the well. 1 7.0 CONCLUSIONS The following conclusions and recommendations are based on the observations and analytical data collected to date. Laboratory analysis of ground water samples indicates significantly reduced levels of gasoline and gasoline constituents in water collected from monitoring well MW-lA. The ' levels reported indicate the continuation of a significant decline that began following completion of the remedial excavation. Significant decreases in MW-6 petroleum hydrocarbon constituent levels were also observed during this sampling event. A review of historical analytical ground water data for monitoring well MW-1/MW-IA ' indicates a dramatic reduction of contaminant mass over the past four years. Since the September 1998 sampling event, contaminant levels have continued to decrease rapidly with reductions between 77% and 99% observed for all analyzed constituents. The ' remedial soil excavation took place between the June 1995 and September 1998 sampling events. Reductions in contaminant levels between 54% and 95% were observed over this period, with the exception of total xylenes which indicated a slight increase of ' approximately 11%. These reductions are summarized in Table 4 and are illustrated on Graph 1. The dramatic reductions observed on this site are attributed to source removal during the remedial excavation, followed by natural attenuation factors that were initially enhanced by the addition of Oxygen Release Compound. Following the depletion of the ORC additional reductions have been documented further demonstrating that natural tattenuation factors are operating, and should continue to operate at this site. American Geological Service,Inc. ' CA95DE-029 j 1